The objectives of this research are to document changes in medical insurance coverage between 1977 and 1987, and to estimate, using a multivariate framework, the antecedents of changes in employer sponsored coverage. The problems faced by the working poor are of particular interest because they constitute the majority of the uninsured. They work in jobs least likely to offer employer - sponsored insurance, yet often do not qualify for public programs. (1) Compare the relative changes over time in both the extent and sources of medial insurance coverage, and the change in the percentage of completely uninsured, among employed individuals classified as: (a) "working-poor" (income below the federally defined poverty line adjusted for year and family size); (b) "economically vulnerable" (incomes up to, and including 200% of the poverty line); and (c) non-poor" (over 200% of the poverty line) this will be achieved with the standard difference test. (2) Explain why employer-sponsored medical insurance has declined, comparing the contributions of both human capital and structural variables to the change. The rate decomposition method will be employed. (3) Test for whether the explanatory structures are the same in 1977 and in 1987 in predicting employer-sponsored medical coverage among three subsamples: (a) the working-poor; (b) economically vulnerable; and (c) the non-poor. This will be achieved with a multinomial logit model with unordered qualitative variables.